JP2011008005A - Light diffusion plate and backlight device using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a light diffusion plate excellent in diffusing performance.SOLUTION: The diffusion plate 10 is formed by sealing a diffusion layer 3 comprising a polymer material 4 and a liquid crystal material 5 between a pair of opposed transparent upper and lower substrates 1, 2 through a sealing member 7. The polymer material 4 is irradiated with an ultraviolet ray to form a three dimensional mesh-like polymer dispersion structure and the liquid crystal material in which the difference of a refractive index between a normal light refractive index and an abnormal light refractive index is 0.15-0.3 is dispersed in the polymer dispersion structure. The back light structure is formed by arranging the light diffusion plate 10 on the upper part of a prism sheet.

Description

  The present invention relates to a diffusion plate having high light diffusibility and a backlight device using the same.

In recent years, light-emitting diodes (hereinafter referred to as LEDs) have been used in various devices such as notebook computers, mobile phones, and PDAs because of their low power consumption and the ability to reduce size and thickness. Lighting has become widespread.
Especially, the backlight apparatus of the display apparatus using a liquid crystal display panel has been widely used under various structures.

The backlight structure shown in FIG. 6 shows the direct type backlight unit shown in Patent Document 1 below. FIG. 6 is a side view of the backlight structure rewritten so as not to depart from the gist thereof for easy explanation.
In FIG. 6, reference numeral 130 denotes a liquid crystal display panel from the top. The liquid crystal display panel 130 has a liquid crystal layer sandwiched between a first substrate 131 and a second substrate 132 made of glass having electrodes for forming pixels on the inner surface, and a first polarizing plate 136 on the outer surface. The second polarizing plate 137 is provided.

An optical compensation sheet laminate 120 is disposed on the back side of the liquid crystal display panel 130. The optical compensation sheet laminate 120 is formed by laminating a first diffusion sheet 121, a first prism sheet 122, a second prism sheet 123, and a second diffusion sheet 124 in this order.
A light guide plate 111 is disposed on the back side of the optical compensation sheet laminate 120 with a first air layer 141 interposed therebetween, and a plurality of disc-shaped light diffusion plates 112 are bonded to the lower surface of the light guide plate 111 with an adhesive. Is provided.

  A plurality of LEDs 103 of R (red), G (green), and B (blue) are arranged on the back surface of the light guide plate 111 with the second air layer 142 interposed therebetween. The LEDs 103 of R, G, and B are provided in the LED array 102, and the LED array 102 is held on the reflection plate 101 by adhesion.

  The disc-shaped light diffusion plate 112 provided on the light guide plate 111 is provided directly above the LED 103 and also serves to reflect and scatter the light of the LED 103 into the second air layer 142. That is, since the LED 103 emits point light, it has the highest luminous intensity on the optical axis. Therefore, the disk-shaped light diffusion plate 112 provided directly above is dispersed and scattered to suppress the light intensity on the optical axis to a low level and improve the uniformity of the light intensity.

  The first prism sheet 122 and the second prism sheet 123 have a shape in which prism grooves are provided in parallel. The first prism sheet 122 and the second prism sheet 123 are orthogonal to each other. Are arranged to be.

  Further, the first diffusion sheet 121 and the second diffusion sheet 124 work to efficiently improve the central luminance in the optical compensation sheet laminate 120 by narrowing the angle of the emitted light diffused from the emission surface of the light guide plate 111. I am letting.

  According to Patent Document 1, it is said that the occurrence of luminance unevenness and chromaticity unevenness is reduced by adopting such a backlight structure.

  With respect to the light diffusing plate and the light diffusing sheet, various configurations are conventionally known. For example, the diffusion plate shown in Patent Document 2 below has a configuration in which a light diffusing agent is dispersed in a propylene polymer. Examples of the light diffusing agent include inorganic particles such as inorganic glass particles, silica particles, aluminum hydroxide particles, calcium carbonate particles, barium sulfate particles, and titanium oxide particles, styrene polymer particles, acrylic polymer particles, and siloxane polymer particles. Organic particles are listed.

  Further, the diffusion plate shown in Patent Document 3 below is a diffusion plate in which a plurality of prism lenses are arranged in parallel, and the prism lens has a cross-sectional shape in which a straight line having four or more oblique sides and a curved vertex are connected symmetrically. It is a diffuser plate having a shape.

  According to Patent Document 3, it is possible to prevent a decrease in luminance and eliminate lamp unevenness by disposing a prism lens diffuser plate on the top of a linear light source such as a cold cathode tube in a direct-type backlight structure. Has been.

Japanese Patent Laid-Open No. 2005-249942 JP 2008-83660 A JP 2008-304501 A

Since the LED is close to point emission, there is a problem that the luminance is very high on the optical axis, the luminance decreases as the distance from the optical axis increases, and the difference in luminance distribution is significant.
The backlight structure shown in Patent Document 1 works to alleviate a significant difference in the luminance distribution of LEDs with a disk-shaped light diffusion plate 112 provided on the lower surface of the light guide plate 111, and further, the first diffusion sheet 121. The second diffusion sheet 124 improves the uniformity of the luminance distribution and the luminance as a whole.
However, the structure of Patent Document 1 is very expensive in terms of cost because there are many parts that constitute the backlight. In addition, the backlight structure has a large thickness, and there is a limit to reducing the thickness.

  Next, the configuration of the diffusion plate disclosed in Patent Document 2 is a configuration in which light diffusion particles are dispersed in a resin. The structure using diffused particles shows light absorbed by the resin and particles, or light that fades while repeating scattering in all directions in the diffuser plate. The problem is that the brightness decreases due to the decrease. Further, it is difficult to completely eliminate the luminance unevenness for a light source having a significant difference in luminance distribution such as an LED.

  In the configuration of the diffusing plate disclosed in Patent Document 3, the prism lens is formed by transferring from a mold, and the shape of the prism lens is determined by the shape accuracy of the mold. Since the shape is complicated, it is difficult to mold the shape of the mold with high accuracy. Therefore, it is difficult to obtain a prism lens with high accuracy.

  The present invention has been made in view of the above-described problems, and an object of the present invention is to provide a diffusion plate that can be manufactured at a low cost, can be bright, and has a uniform luminance distribution.

  As means for solving the problems, the light diffusion plate of the present invention comprises at least a pair of transparent substrates, a transparent polymer material, a liquid crystal material, and a sealing member, and the sealing members are disposed in a pair of opposed transparent substrates. The polymer material and the liquid crystal material are sealed through the film.

  The light diffusion plate of the present invention is characterized in that the polymer material is cured by ultraviolet irradiation.

  The polymer material (monomer) is polymerized by ultraviolet irradiation to form a three-dimensional network polymer network. When a liquid crystal material (for example, a nematic liquid crystal material) is dispersed in the polymer network, the major axes of the liquid crystal molecules are aligned in random directions. That is, when viewed macroscopically, it is in the same state as being oriented in an irregular direction. For this reason, the refractive index of the liquid crystal molecules and the refractive index of the polymer network resin differ, and light scattering, that is, light diffusion occurs.

When a polymer material (monomer) and a liquid crystal material are sealed in a pair of opposed transparent substrates via a sealing member and irradiated with ultraviolet rays, the monomers are polymerized and become a cured state. And the diffusion plate of the flat plate state which becomes a fixed state with a pair of opposing transparent substrate, and a shape does not deform | transform is obtained.
In addition, by using a polymer material having excellent transparency and a liquid crystal material, light absorption can be suppressed to a low level and light utilization efficiency can be increased. In addition, a diffusion plate having excellent diffusibility can be obtained.

  The light diffusing plate of the present invention is characterized in that the liquid crystal material is a liquid crystal material having a refractive index difference in the range of 0.15 to 0.3.

The liquid crystal material is preferably a material having excellent scattering characteristics. Examples of such a liquid crystal material include nematic liquid crystal, and those having a relatively large difference between the extraordinary refractive index and the ordinary refractive index and having a refractive index difference of 0.15 to 0.3 are preferable. When a liquid crystal material having such a difference in refractive index is used, light scattering characteristics appear well.
Further, by using such a liquid crystal material, neither color selective absorption nor selective reflection of the emission color occurs, so that light brightness is suppressed and brightness is improved.

  Moreover, the light diffusing plate of the present invention is characterized in that a gap between a pair of opposed transparent substrates is 10 to 30 μm.

  When the gap is smaller than 10 μm, the scattering effect is reduced and the uniformity of the luminance distribution is lowered. Further, even if the gap is made larger than 30 μm, the scattering effect does not extend much. In consideration of thinning, the range of 10 to 30 μm is preferable.

  Moreover, the light diffusing plate of the present invention is characterized in that it has a portion having a partially different degree of light scattering.

The light diffusion can be adjusted by partially varying the degree of light scattering. For example, when a light source that is an LED is used, since the LED is close to point emission, the luminance on the optical axis is high and the luminance is low on the periphery.
The brightness distribution can be made uniform as a whole by increasing the degree of scattering in the high luminance part and decreasing the degree of scattering in the low luminance part.
In the present invention, a high degree of scattering represents a state where scattering is actively performed, and a low degree of scattering represents a state where there is little scattering. Hereinafter, under this definition, it is expressed that the degree of scattering is large and the degree of scattering is small.

  The light diffusing plate of the present invention is characterized in that a transparent coating film having a refractive index smaller than the refractive index of the transparent substrate is provided on at least one of the upper surface and the lower surface of the light diffusing plate.

  By adopting such a configuration, an antireflection effect is produced, and the amount of light incident on the light diffusion plate can be increased. In addition, a scratch prevention effect can be obtained.

  Moreover, the backlight device using the light diffusing plate of the present invention is characterized in that the light diffusing plate is arranged on the light emitting side of the light source.

  By adopting this arrangement structure, it is possible to control the luminance unevenness of the light emitted from the light source by the light diffusing plate. Further, the luminance can be uniformly suppressed.

  The backlight device using the light diffusing plate of the present invention is characterized in that the light diffusing plate is laminated on the lower surface side polarizing plate of the liquid crystal display panel and integrated with the polarizing plate.

  By integrating the light diffusing plate with the polarizing plate, the viewing angle of the display image on the liquid crystal display panel can be widened. Further, an effect of thinning the liquid crystal display panel provided with the backlight device can be obtained.

  According to the light diffusing plate of the present invention, the diffusing performance is enhanced and a bright and uniform luminance distribution is obtained. Further, a backlight structure can be obtained at a low cost.

It is the principal part sectional view typically shown of the light diffusing plate concerning the embodiment of the present invention, and the explanatory view showing typically the function. FIG. 2 is an explanatory diagram schematically illustrating a light diffusion state in the light diffusion plate illustrated in FIG. 1. 1 is a side view schematically showing a backlight device provided in a liquid crystal display panel according to Embodiment 1. FIG. It is principal part sectional drawing which showed typically the light diffusing plate in FIG. 5 is a side view schematically showing a backlight device provided in a liquid crystal display panel according to Embodiment 2. FIG. It is a side view of the direct type backlight unit shown by patent document 1. FIG.

  Hereinafter, embodiments for carrying out the present invention will be described with reference to FIGS. FIG. 1 is a cross-sectional view schematically showing a main part of a light diffusing plate according to an embodiment of the present invention and an explanatory diagram schematically showing its function. FIG. 2 is an explanatory diagram schematically showing the light diffusion state in the light diffusion plate shown in FIG.

  In FIG. 1, 1 is a transparent upper substrate, 2 is a transparent lower substrate, and it forms a pair of transparent substrates facing each other. 3 is a diffusion layer, 4 is a transparent polymer material, and 5 is a liquid crystal material. The polymer material 4 forms a three-dimensional network polymer network (not shown) by ultraviolet irradiation, and the liquid crystal material 5 is dispersed in the three-dimensional network to form the diffusion layer 3. That is, the diffusion layer 3 has a polymer dispersion type structure. Reference numeral 7 denotes a sealing member, and reference numeral 10 denotes a light diffusion plate. N represents incident light, Pm represents forward scattered outgoing light, and Pn represents back scattered outgoing light.

  The light diffusing plate 10 shown in FIG. 1 seals the polymer material 4 and the liquid crystal material 5 constituting the diffusing layer 3 with a sealing member 7 in a predetermined gap between the opposing upper and lower substrates 1 and 2. The polymer material is polymerized by irradiating ultraviolet rays to form a three-dimensional network polymer network. That is, it has a structure of a polymer dispersion type diffusion plate.

In the present invention, a mixed material of a polymer material (monomer) and a liquid crystal material (for example, a nematic liquid crystal material), that is, a liquid crystal material in PDLC (Polymer Dispersed Liquid Crystal) mode is used. The monomers are polymerized by ultraviolet irradiation to form a three-dimensional network polymer network, and the liquid crystal material is dispersed in the polymer network.
Therefore, as shown in FIG. 1, the major axis of the liquid crystal molecules of the liquid crystal material 5 is aligned in a random direction. That is, when viewed macroscopically, the liquid crystal molecules are in the same state as aligned in an irregular direction.
For this reason, the refractive index of the liquid crystal molecules and the refractive index of the polymer network resin are different, and light scattering occurs.

Here, a transparent polymer is used as the polymer material (monomer) 4, and examples of the polymer include an ultraviolet curable acrylic resin, and in particular, an acrylic monomer and an acrylic oligomer that are polymerized and cured by ultraviolet irradiation. preferable.
Among these, a photocurable acrylic resin having a fluorine group is preferable because it can produce a light modulation layer with good scattering characteristics and hardly changes with time. Such materials include 2-ethylhexyl acrylate, 2-hydroxyethyl acrylate, neopentyl glycolide acrylate, hexanecidiol diacrylate, diethylene glycol diacrylate, polyethylene glycol diacrylate, and tripropylene glycol diacrylate.

Next, the liquid crystal material 5 is preferably a nematic liquid crystal, a smectic liquid crystal, or a cholesteric liquid crystal, and may be a single or a mixture containing two or more kinds of liquid crystalline compounds.
As the nematic liquid crystal, a cyanobiphenyl nematic liquid crystal having a relatively large difference between the extraordinary refractive index and the ordinary light refractive index, or a fluorine-based or chloro-based nematic liquid crystal that is stable over time is preferable. A nematic liquid crystal is most preferable because it has good scattering characteristics and hardly changes with time.

The liquid crystal material 5 preferably has a normal light refractive index of 1.49 to 1.54 and a difference in refractive index between the extraordinary light refractive index and the ordinary light refractive index of 0.15 to 0.30. Even if the refractive index difference is smaller or larger than this range, the scattering effect cannot be obtained.
Among them, a chloro nematic liquid crystal having a normal light refractive index of 1.50 to 1.53 and a refractive index difference of 0.2 to 0.30 can be mentioned as a preferable example.

  The mixing ratio of the liquid crystal material 5 in the diffusion layer 3 is generally about 30 to 90% by weight, less than 30%, and more than 90% makes it impossible to take a volume difference between the polymer material and the liquid crystal material. Scattering characteristics are reduced.

Irradiation with ultraviolet rays is performed after a mixed material (a mixed material of a polymer material and a liquid crystal material) is sealed in a pair of substrates.
For the ultraviolet irradiation, a mercury lamp is used, and the temperature is usually set to about 40 ° C., the intensity is set to 20 to 80 mW / cm ² , and the time is set appropriately in consideration of the scattering characteristics in the range of 30 to 120 seconds. Is good.

The pair of upper and lower substrates 1 and 2 is made of transparent glass or transparent resin film. As the glass, soda glass, quartz glass, borosilicate glass, ordinary plate glass, or the like is used. The plate thickness of the glass is not particularly limited, but it is possible to use a thin one having a thickness of about 200 μm.
Moreover, when using a resin film, the resin film excellent in moisture resistance, impact resistance, chemical resistance, etc. is used. As such a thing, resin films, such as a polyethylene terephthalate (PET) resin, a polycarbonate resin, a polyimide resin, a polystyrene resin, a polyethylene resin, are mentioned, for example. The thickness of the film is not particularly limited, but a film having a thickness of 100 μm or more can be used.

The sealing member 7 is formed of a thermosetting resin such as an epoxy resin or an acrylic resin, or an ultraviolet curable resin. Although not shown, a spacer in which spacers such as spacer balls are dispersed is used to form a predetermined thickness. A sealing member is formed on one of the upper substrate 1 and the lower substrate 2 by a method such as a printing method in a state where an opening is provided in a part, and the upper and lower substrates 1 and 2 are bonded together with a predetermined gap, The sealing member is cured by a baking method or an ultraviolet irradiation method.
Then, the mixed material of the polymer material 4 and the liquid crystal material 5 is injected into the gap between the upper and lower substrates 1 and 2 from a part of the opening, and the opening is closed with an ultraviolet curable resin after the injection. 2, the polymer material 4 and the liquid crystal material 5 are sealed.

Here, the gap between the upper and lower substrates 1 and 2 is preferably in the range of 10 to 30 μm. When the gap is smaller than 10 μm, the degree of light scattering is reduced and the diffusibility is lowered. On the other hand, if the gap is larger than 30 μm, the scattering degree is saturated and the diffusion effect is not extended. Moreover, when it is thick, a problem of workability arises. For example, when the upper and lower substrates 1 and 2 are formed of a resin film, the cutting processability is deteriorated. Further, when the thickness is increased, the amount of liquid crystal material and polymer material used is increased, resulting in a problem of cost increase.
By setting the gap in the range of 10 to 30 μm, it is possible to contribute to thinning.

Next, when the incident light N indicated by an arrow enters the light diffusing plate 10 having the above configuration, scattering occurs in the diffusion layer 3, and the forward scattered outgoing light Pm is dispersed on the upper side (front side) in the drawing. Then exit. At the same time, the backscattered outgoing light Pn also appears on the incident side (rear side) of the incident light N.
The light dispersion characteristics of the polymer dispersion type diffusion plate having the above-described structure are as shown in FIG. FIG. 2 schematically shows a distribution state of luminous intensity due to the diffusion of vertical light and near-normal incident light in the diffuser plate at a portion O where the diffuser plate is present, and Q is a luminous intensity distribution curve. is there. 90 ° indicates the vertical direction in the region O. In the distribution curve Q, A represents the maximum luminance point on the left side of the region O, C represents the maximum luminance point on the right side, and B represents the luminance on the 90 ° line.
As can be seen from FIG. 2, the light is dispersed in such a manner that it has directivity in two directions from the portion O to the left and right. And it shows the distribution of luminous intensity just like a camel hump.

In the polymer dispersion type diffusion plate, the degree of scattering can be changed by adjusting the irradiation condition of ultraviolet rays. For example, when the irradiation intensity of ultraviolet rays is increased, the degree of light scattering increases, and when the intensity is decreased, the degree of light scattering decreases.
This will be explained using the luminance distribution curve Q. When the degree of light scattering increases, the value of point B decreases and the distance between ACs increases. That is, the luminous intensity at the part O decreases, the distance between the two maximum points B and C increases, and the range of diffusion increases.
On the other hand, as the degree of light scattering decreases, the value at point B increases and the distance between ACs decreases. That is, the luminous intensity at the part O is increased, the distance between the two maximum points B and C is narrowed, and the diffusion range is narrowed.

  As described above, by setting appropriate irradiation conditions in consideration of the directivity characteristics and luminous intensity characteristics of the light source, the degree of scattering can be adjusted to be uniform. This has the effect of making the brightness uniform.

  In the light diffusing plate 10 shown in FIG. 1, ultraviolet irradiation is performed with the same intensity as a whole. However, in consideration of the directivity characteristics and luminous intensity characteristics of the light source, the irradiation intensity is increased in a portion with high luminous intensity. If the degree of scattering is increased and the irradiation intensity is reduced in the portion with low luminous intensity to reduce the degree of scattering, the luminous intensity can be suppressed uniformly. That is, the luminance can be suppressed uniformly.

Further, since a transparent polymer material and a liquid crystal material are used, light absorption is small, and color selective absorption and selective reflection of light emission color do not occur, so that attenuation and dimming of light can be suppressed.
This has the effect of increasing brightness by increasing the amount of light emitted from the diffusion plate.

Further, by providing a coating film having a refractive index smaller than the refractive index of the upper and lower substrates 1 and 2 on the outer surface of the light diffusing plate 10 shown in FIG. 1 on the light incident side, light reflection from the diffusing plate 10 is reduced. Incident light on the diffusion plate 10 can be increased. This increases the amount of light emitted from the diffusion plate 10 and produces an effect of increasing luminance.
Moreover, by having a coating film, it also serves to prevent the diffusion plate 10 from being scratched.

  Hereinafter, further details of the present invention will be described in the following examples.

  A light diffusing plate according to the first embodiment and a backlight device using the light diffusing plate will be described with reference to FIGS. FIG. 3 is a side view schematically showing the backlight device provided in the liquid crystal display panel according to the first embodiment. FIG. 4 is a cross-sectional view schematically showing the main part of the light diffusion plate in FIG. . Note that components having the same specifications as the components in the above-described embodiment are given the same reference numerals, and the detailed description thereof is limited to the necessary limit.

  First, the reference numerals shown in FIG. 3 will be sequentially described from the bottom of the figure. 21 is a light source mounting substrate, and 22 is a light source. In the first embodiment, the light source 22 uses an LED, and the mounting substrate 21 uses an FPC. A plurality of LED light sources 22 are mounted on the FPC mounting substrate 21 so as to be aligned at equal intervals. Light emitted upward is emitted from the light source 22 as an LED, as indicated by an arrow.

Reference numerals 25a and 25b denote prism sheets. This prism sheet is a sheet that is provided with a groove having a triangular cross section in parallel to form a prism lens. The prism sheets 25a and 25b have the same lens shape and the same size, and the prism sheets 25a and 25b are laminated with the grooves orthogonal to each other.
By superimposing the prism sheets 25a and 25b in an orthogonal state, the incident light from the LED light source 22 enters the light diffusing plate in a state close to vertical light.

  Reference numeral 10 denotes the light diffusion plate described in the above embodiment. Reference numeral 11 denotes a coating film. In Example 1, the coating film 11 is provided on the lower surface of the light diffusing plate 10. The coating film 11 is provided for the purpose of preventing reflection and serves to increase the amount of light incident on the light diffusion plate 10.

Here, the emitted light in a state close to the vertical light from the prism sheets 25a and 25b is incident light to the light diffusion plate 10, but the emitted light as Pa indicated by the arrow is directly above the light source 22 as the LED. Since the LED emits point light, the luminous intensity on the optical axis is high. Therefore, in the figure, Pa is indicated by a long arrow line.
Also, the emitted light Pb indicated by the arrow points to the emitted light of the part located in the middle of the adjacent LEDs, and the emitted light Pb of this part is separated from the adjacent LEDs by distance, so the luminous intensity is Low. Therefore, in the figure, it is indicated by a short arrow line.

Next, 30 is a liquid crystal display panel. Further, 31 is an upper transparent substrate, 32 is a lower transparent substrate, 37 is a sealing member, 38 is an upper polarizing plate, and 39 is a lower polarizing plate.
In the liquid crystal display panel 30, an upper transparent substrate 31 having a transparent electrode and an alignment film formed on the lower surface and a lower transparent substrate 32 having a transparent electrode and an alignment film formed on the upper surface are arranged facing each other with a certain gap therebetween. The liquid crystal material is sealed through the sealing member 37 in the gap. In some cases, a color filter or the like is provided in the upper and lower substrates 31 and 32.
Further, the upper polarizing plate 38 is provided on the upper surface of the upper transparent substrate 31, and the lower polarizing plate 39 is provided on the lower surface of the lower transparent substrate 32.

In the backlight device of the present invention, a light diffusing plate 10 provided with an FPC mounting substrate 21, an LED light source 22, prism sheets 25a and 25b, and a coating film 11 is a main component.
Further, this backlight device is a direct type backlight device in which a light source 22 is disposed directly below the liquid crystal display panel 30.
Although not shown, this backlight device is housed and held in a housing.

The light diffusing plate 10 of Example 1 has the same configuration as the light diffusing plate in the above-described embodiment as a component configuration, but the strength of the ultraviolet irradiation intensity is increased, and a portion having a large degree of scattering is partially included. A small part is provided.
FIG. 4 schematically shows this state. In FIG. 4, 3 is a diffusion layer, 3a is a layer with a high degree of scattering, 3b is a layer with a low degree of scattering, and the diffusion layer 3 is an alternating layer 3a with a high degree of scattering and a layer 3b with a low degree of scattering. Are lined up.

The layer 3a having a high degree of scattering is obtained by increasing the irradiation intensity of ultraviolet rays as described in the above embodiment, and the layer 3b having a low degree of scattering is obtained by reducing the irradiation intensity of ultraviolet rays. Can do.
Further, the adjustment for increasing or decreasing the irradiation intensity can be performed by using an ultraviolet absorption mask that partially differs in the amount of absorbed ultraviolet rays.
For example, if a portion containing no UV absorber and a mask containing UV absorber dispersed therein are prepared, and the mask is placed on the light diffusion plate 10 and irradiated with UV rays, the UV absorber is included. The part where there is no ultraviolet ray has a high irradiation intensity, and the part where the UV absorber is dispersed absorbs the ultraviolet ray, so the irradiation intensity is low.
As described above, when the ultraviolet absorption mask is used, the irradiation intensity can be adjusted in any number of steps. In addition, continuous irradiation intensity adjustment is possible.

In FIG. 4, the layer 3a having a high degree of scattering is formed in the region of the long arrow line Pa, and the layer 3b having a low degree of scattering is formed in the region of the short arrow line Pb.
Since the LED of the light source 22 is point emission, the luminous intensity on the optical axis is high. That is, since the portion located directly above the LED has a high luminous intensity, it is necessary to increase the degree of scattering. Therefore, a layer 3a having a high degree of scattering is provided in the region located directly above the LED (the region indicated by the long arrow line Pa).
On the other hand, the region part (region part of the short arrow line Pb) located in the middle of both adjacent LEDs has a low luminous intensity. Therefore, a layer 3b having a small degree of scattering is provided in this region to suppress the degree of scattering to a low level so that the luminous intensity does not decrease much.

  By making the structure of the light diffusing plate 10 the layer 3a having a high degree of scattering and the layer 3b having a low degree of scattering as described above, the light diffusion can be made uniform as a whole, and the luminance can be made uniform. Can be achieved.

In the first embodiment, the light diffusion plate 10 is provided with a coating film 11 on the light incident side. The coating film 11 is provided for the purpose of preventing reflection, and more incident light from the lower side is incident on the light diffusion plate 10.
The coating film 11 is formed of a material having a refractive index smaller than that of the lower substrate 2 of the light diffusion plate 10. For example, when glass (refractive index: 1.52), PET film (refractive index: 1.64) or the like is used for the lower substrate 2, an acrylic resin or silicone resin having a lower refractive index than that is a coating film. It can be mentioned as a material. In addition, there are various commercially available antireflection coating materials. For example, there are 1.3 to 1.7 siloxane skeleton resin manufactured by Sekisui Chemical Co., Ltd., and multilayer antireflection coating material manufactured by Nissan Chemical Industries.
In addition to preventing reflection, the coating film 11 also serves to protect the light diffusion plate 10 from damage such as scratches.

In the first embodiment, the light diffusion plate 10 has a structure in which the light diffusion plate 10 is bonded to the lower polarizing plate 39 of the liquid crystal display panel 30 and integrated with the lower polarizing plate 39.
The light dispersed by the light diffusion plate 10 passes through the lower polarizing plate 39 and illuminates the display image on the liquid crystal display panel 30. By illuminating the display image with dispersed light, an effect of widening the viewing angle of the image is obtained. In addition, clearness appears in the display image.

In the first embodiment, the light diffusing plate 10 is disposed on the prism sheets 25a and 25b.
In the polymer-dispersed light diffusing plate 10, it is desirable that light in a state close to vertical light is incident on the entire diffusing plate in order to improve light scattering characteristics. As shown in FIG. 3, the light diffusing plate 10 is provided on the prism sheets 25a and 25b, so that the effect of sufficiently increasing the scattering characteristics of the light diffusing plate 10 is produced.

  In FIG. 3, although the gap between the prism sheets 25a and 25b and the light diffusing plate 10 is shown in a separated state, it is not always necessary to provide a large gap. And the light diffusion plate 10 may be laminated.

By adopting the above configuration, it is possible to obtain backlight illumination that is bright with a single diffuser plate and under uniform luminance. Compared with the structure of the prior art, the number of components is reduced, and the backlight structure can be formed at a low cost.
Also, the diffusion plate itself is a few components, and since the forming method is easy, the diffusion plate can be formed at a low cost.

  Next, a backlight device according to Example 2 will be described with reference to FIG. FIG. 5 is a side view schematically showing a backlight device provided in the liquid crystal display panel according to the second embodiment. In addition, the same code | symbol is attached | subjected to the component which makes the same specification as the structure of above-mentioned Example 1. FIG.

  A feature of the backlight device of the second embodiment is a backlight structure using a light guide plate. In addition, the lower polarizing plate of the liquid crystal display panel is separated from the liquid crystal display panel and is integrally provided on the light diffusion plate.

Specifically, in FIG. 5, reference numeral 41 denotes a light guide plate, and an LED light source 22 provided on the FPC mounting substrate 21 is arranged on the side surface of the light guide plate 41.
The light guide plate 41 is made of acrylic resin or the like, has a plate shape, and the lower surface has an inclined surface. Although not shown in the figure, a configuration is provided in which reflecting means and diffusing means are provided on the lower surface side.
The light incident from the light source 22 is reflected and diffused in the light guide plate and is emitted to the upper surface side of the light guide plate 41.

On the upper surface side of the light guide plate 41, prism sheets 25a and 25b are provided in a laminated manner, and the light diffusion plate 10 in which the coating film 11 and the lower polarizing plate 39 are integrally provided is disposed on the prism sheets 25a and 25b. is doing.
The prism sheets 25a and 25b, the coating film 11, the light diffusing plate 10, and the lower polarizing plate 39 are structurally the same as those in the configuration of the first embodiment, but the diffusing layer of the light diffusing plate 10 is the same. The whole surface is formed by irradiating with ultraviolet rays under the same conditions. Therefore, there are no layers with a large or small light scattering degree in the diffusion layer, and the scattering degree of the diffusion layer is all uniform.

In the second embodiment, the lower polarizing plate 39 constituting the liquid crystal display panel 30 is separated from the lower transparent substrate 32 of the liquid crystal display panel 30, and the light diffusing plate 10 is bonded to the upper surface of the light diffusing plate 10 with an adhesive. Provided integrally.
Therefore, a gap is provided between the lower transparent substrate 32 of the liquid crystal display panel 30 and the lower polarizing plate 39 provided on the upper surface of the light diffusion plate 10.

By providing a gap between the lower transparent substrate 32 and the lower polarizing plate 39, the diffusion range of the light diffused by the light diffusing plate 10 is further expanded while passing through the gap, and enters the liquid crystal display panel 30. . For this reason, the viewing angle of the display image of the liquid crystal display panel 30 can be further expanded. In addition, the display image is also clearly visible.
Note that the larger the gap amount, the wider the viewing angle. However, since it affects the overall thickness, it is preferably set appropriately within an allowable range.

  In FIG. 5, a gap is provided between the light guide plate 41 and the prism sheets 25a and 25b and between the prism sheets 25a and 25b and the light diffusion plate 10, but the drawing is not necessarily large. There is no need to provide a gap, and the light guide plate 41, the prism sheets 25a and 25b, and the light diffusion plate 10 may be simply laminated.

  The light guide plate 41 is formed of a light guide plate having an inclined bottom surface, but is not particularly limited in shape, and there is no problem even if a light guide plate having another shape is used.

In addition, in the case where significant luminance unevenness occurs in the light emitted from the light guide plate 41, it is also possible to provide another light diffusion plate between the light guide plate 41 and the prism sheets 25a and 25b.
The light diffusing plate is a diffusing plate whose scattering degree can be adjusted according to the luminance distribution of the light emitted from the light guide plate. A diffusion layer in which a layer having a high degree of scattering and a layer having a low degree of scattering are provided corresponding to the luminance distribution. It should be a board.
In this way, by providing a diffusion plate capable of adjusting the degree of scattering between the light guide plate 41 and the prism sheets 25a and 25b, luminance unevenness is suppressed, and a uniform amount of light is incident on the prism sheets 25a and 25b. Can do.

DESCRIPTION OF SYMBOLS 1 Upper substrate 2 Lower substrate 3 Diffusion layer 4 Polymer material 5 Liquid crystal material 7 Sealing member 10 Light diffusing plate 11 Covering film 21 Mounting substrate 22 Light source 25a, 25b Prism sheet 30 Liquid crystal display panel 31 Upper transparent substrate 32 Lower transparent substrate 37 Sealing member 38 Upper polarizing plate 39 Lower polarizing plate 41 Light guide plate

Claims (8)

  At least a pair of transparent substrates and a transparent polymer material, a liquid crystal material, and a sealing member, and the polymer material and the liquid crystal material are sealed in the pair of transparent substrates facing each other through the sealing member A light diffusion plate characterized by that.   The light diffusion plate according to claim 1, wherein the polymer material is cured by ultraviolet irradiation.   The light diffusing plate according to claim 1, wherein the liquid crystal material is a liquid crystal material having a refractive index difference in a range of 0.15 to 0.3.   The light diffusion plate according to claim 1, wherein a gap between the pair of opposed transparent substrates is 10 to 30 μm.   5. The light diffusing plate according to claim 1, wherein the light diffusing plate has a portion having a partially different light scattering degree.   6. The light diffusing plate according to claim 1, wherein at least one of an upper surface and a lower surface of the light diffusing plate has a transparent coating film having a refractive index smaller than that of the transparent substrate. A light diffusing plate characterized by A backlight device using the light diffusing plate according to any one of claims 1 to 6,
A backlight device, wherein the light diffusing plate is disposed on a light emitting side of a light source.   The backlight device according to claim 7, wherein the light diffusion plate is laminated on a lower surface side polarizing plate of a liquid crystal display panel and integrated with the polarizing plate.

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